The present invention relates to a separation apparatus of the isotopes with different mass numbers, and more particularly to a laser isotbpe separation apparatus.
For example, natural palladium contains the isotopes with mass numbers 102 (1%), 104 (11%), 105 (22.2%), 106 (27.3%), 108 (26.7) and 110 (11.8%). The palladium in the insoluble residue from the reprocessing of spent fuel contains the isotopes of the mass number 107 by 18%, for example, in addition to the isotopes of the above mass numbers. There is strong demand on the effective method to selectively separate the isotopes of platinum group elements. (For example, only the palladium with mass number 107 is radioactive, and if this can be selectively removed, the palladium in the insoluble residue from the reprocessing of spent fuel can be effectively utilized as valuable resources.) Laser isotope separation method is known as a means to separate isotopes. By this method, the substance containing isotopes is gasified, and linearly-polarized laser light is applied to selectively excite only the desired isotopes by isotope shift. Further, laser beam is applied on the atoms selectively excited, and the ionized atoms are separated from the other neutral isotopes by means of the electrode applied with electric field or magnetic field.
Taking an example in uranium, the principle of the conventional laser isotope separation method is described below. In the schematical illustration of FIG. 8, when linearly-polarized laser light of .lambda..sub.1 (.about.591 nm) is applied to the uraniums 235 and 238 on ground level, only uranium 235 absorbs light because of the isotope shift (280 milli cm.sup.-1) and is excited to the first excited level, while uranium 238 does not absorb light and is not excited. When the linearly-polarized laser light of .lambda..sub.2 (.about.563 nm) is applied on uranium 235 it is excited from the above excited level to the intermediate excited level. It is further excited to higher than the ionized potential (I.P.) by the third light (.lambda..sub.3 =625 nm) and is ionized. On the other hand, uranium 238 is not excited at all. Accordingly, in the gas containing ionized uranium 235 and neutral uranium 238, the former can be separated from the latter by means of the electrode applied with electric field or magnetic field.
Meanwhile, it is known that the isotope shift depends upon the mass number of the element as shown in the graph of FIG. 5. From the mass number of about 100 up, isotope shift increases with the increase of mass number due to volume effect of atoms, while the isotope shift increases due to mass effect of atoms when the mass number decreases. As it is evident from this graph, the isotope shift is very small near the palladium with mass number of 102 to 110. Actually, it is about 8 milli cm.sup.-1. In contrast, the line width of laser light is about 30 milli cm.sup.-1. Thus, when the method of FIG. 8 is applied on the element with mass number of about 100, the isotopes cannot be selectively excited because the isotope shift is smaller than the line width of laser light.